<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box {
            width: 5px;
            height: 5px;
            border: 1px solid #333;
            border-top: transparent;
            border-left: transparent;
            transform: rotateZ(-45deg)
        }

        .box:hover {
            transform: rotateZ(45deg)
        }
    </style>
</head>

<body>
    <div class="box"></div>
</body>

</html>